Method and apparatus for fabricating rotary cone drill bits

ABSTRACT

A method and apparatus are provided for use in fabricating rotary cone drill bits from multiple drill bit segments. Each drill bit segment (40) preferably includes a first portion (50) with mating surfaces (61, 62) designed to be aligned with mating surfaces (61, 62) of other drill bit segments (40) and a second portion (80) which includes a support arm (90) with a cutter cone assembly (100) rotatably mounted thereon. A recess (70) having a generally spherical surface is formed within the first portion (50) of each drill bit segment (40) such that when the respective drill bit segments (40) are aligned with each other, the spherical recesses (70) cooperate with each other to define a generally spherical cavity. A ball (72) is disposed within the resulting spherical cavity when the drill bit segments are joined with each other to form the bit body (42) for the resulting rotary cone drill bit (20). The ball (72) and spherical recesses (70) cooperate with each other to allow alignment of the respective drill bit segments (40) relative to each other prior to welding.

RELATED APPLICATION

This application claims the benefit of previously filed provisionalPatent Application Ser. No. 60/075,743 filed Feb. 23, 1998 entitled"Method and Apparatus for Fabricating Rotary Cone Drill Bits."

TECHNICAL FIELD OF THE INVENTION

The present invention relates generally to drill bits used in drillingboreholes in the earth, and more particularly to a method and apparatusfor fabricating a rotary cone drill bit from multiple drill bitsegments.

BACKGROUND OF THE INVENTION

Various types of rotary drill bits or rock bits may be used to form aborehole in the earth. Examples of such rock bits include roller conedrill bits or rotary cone drill bits used in drilling oil and gas wells.A typical roller cone drill bit includes a bit body with an upper endadapted for connection to a drill string. A plurality of drill bitsegments, typically three, is frequently used to form the bit body. Eachdrill bit segment preferably includes a support arm which extends from alower end of the bit body. Each support arm also includes a spindle orjournal protruding generally radially inward and downward with respectto a projected rotational axis of the bit body. An enlarged generallycylindrical cavity is preferably formed in the bit body to receivedrilling fluids from the drill string.

A cutter cone assembly is generally mounted on each spindle androtatably supported on bearings acting between the spindle and theinterior of a cavity or chamber formed within each cutter cone assembly.One or more nozzle housings may be formed on the bit body adjacent tothe support arms. A nozzle is typically positioned within each housingto direct drilling fluid passing downwardly from the drill stringthrough the bit body toward the bottom of the borehole being formed.Drilling fluid is generally provided by the drill string to performseveral functions including washing away material removed from thebottom of the borehole, cleaning the cutter cone assemblies, andcarrying the cuttings radially outward and then upward within an annulusdefined between the exterior of the bit body and the wall of theborehole.

Various techniques have previously been used to weld or attach the drillbit segments with each other to form a rotary cone drill bit. U.S. Pat.No. 4,054,772, entitled "Positioning System for Rock Bit Welding" showsapparatus for positioning three drill bit segments relative to eachother followed by laser welding to join the drill bit segments with eachother to form a bit body with three support arms and respective cuttercone assemblies extending therefrom.

U.S. Pat. No. 3,907,191, entitled "Method of Constructing a Rotary RockBit" discloses a method and apparatus for constructing a rotary conerock bit with an accurate gauge size from multiple drill bit segments.The '191 Patent discloses "scissoring" of drill bit segments relative toeach other to establish the desired gauge diameter for the resultingrotary cone drill bit.

U.S. Pat. No. 3,987,859, entitled "Unitized Rotary Rock Bit" discloses amethod and apparatus for positioning drill bit segments relative to eachother to allow an electron beam gun to form a rotary cone drill bit bywelding the segments with each other. The '859 Patent also showsinserting a dowel in adjacent holes in the respective drill bit segmentsto aid in aligning the drill bit segments with each other prior towelding.

U.S. Pat. No. 4,045,646, entitled "Positioning Fixture for Rock BitWelding" discloses an apparatus which may be satisfactorily used toposition drill bit segments relative to each other and to weld adjacentdrill bit segments with each other to form a rotary cone drill bit.

U.S. Pat. No. 4,414,734 entitled "Triad for Rock Bit Assembly" shows atriad which may be positioned in respective holes in three drill bitsegments to assist with aligning the drill bit segments with each otherprior to welding.

SUMMARY OF THE INVENTION

In accordance with teachings of the present invention, disadvantages andproblems associated with fabrication and assembly of previous rotarycone drill bits from multiple drill bit segments have been substantiallyreduced or eliminated. In one aspect of the present invention, threedrill bit segments are provided with each drill bit segment havingrespective mating surfaces that cooperate with each other to allowwelding each drill bit segment to adjacent drill bit segments to form abit body. A generally spherical recess is preferably formed in eachdrill bit segment. During assembly of the drill bit segments inpreparation for welding, a ball is preferably placed in the sphericalrecess of one drill bit segment. The drill bit segments are thenpositioned adjacent to each other such that the associated sphericalrecesses cooperate with each other to form a generally closed sphericalcavity to trap the ball therein.

In accordance with teachings of the present invention, multiple drillbit segments are provided with each drill bit segment having a generallyirregular, elongated configuration defined in part by an interiorsurface and an exterior surface. Two mating surfaces are preferablyformed on the interior of each drill bit segment with the matingsurfaces disposed at an angle of approximately 120° relative to eachother. The mating surfaces extend from a first end of each drill bitsegment to a location intermediate a second end of the respective drillbit segment. A generally spherical recess is preferably formed in theinterior surface of each drill bit segment at a junction between therespective mating surfaces intermediate the first end and the second endof the respective drill bit segment.

Technical advantages of the present invention result from placing a ballwithin generally spherical recesses formed respectively on the interiorsurface of multiple drill bit segments with each drill bit segmenthaving a spindle or journal with a cutter cone assembly rotatablymounted thereon. The ball and the spherical recesses cooperate with eachother to maintain the desired longitudinal spacing of the cutter coneassemblies relative to each other to prevent cone interference whilepositioning the drill bit segments relative to each other prior towelding. The spherical recesses and the ball cooperate with each otherto maintain the desired cone height and the desired gauge diameter ofthe resulting rotary cone drill bit within acceptable limitations. Theball and spherical recesses also cooperate with each other to establisha pivot point within the interior of the associated drill bit segmentsto allow adjusting the position of the drill bit segments relative toeach other prior to welding while maintaining relative concentricalignment of the drill bit segments relative to each other and aprojected axis of rotation for the resulting drill bit. One result ofthis generally concentric alignment is maintaining a more uniform wallthickness of an enlarged, generally cylindrical cavity formed in the bitbody during threading of the bit body.

Further technical advantages of the present invention includemaintaining desired dimensional tolerances of drill bit diameter andlocation of the cutter cone assemblies relative to the drill bit bodyeven though the dimensions of the drill bit segments used to assemblethe resulting drill bit may have less than desired dimensionaltolerances. As a result of fabricating rotary cone drill bits frommultiple drill bit segments in accordance with teachings of the presentinvention, the scrap rate for drill bits noncompliance with dimensionaltolerances is decreased and the resulting drill bits have improveddownhole performance due to enhanced dimensional integrity correspondingwith the original design dimensions for the associated rotary cone drillbit. Assembling a rotary cone drill bit in accordance with teachings ofthe present invention substantially reduces or eliminates variationsbetween originally designed dimensions and the as-built dimensions ofthe resulting rotary cone drill bit. Teachings of the present inventionsubstantially reduce or eliminate scrap and rework associated withfabricating rotary cone drill bits from multiple drill bit segments.

Other technical advantages of the present invention will be readilyapparent to one skilled in the art form the following figures,description, and claims.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present invention, and theadvantages thereof, reference is now made to the following briefdescriptions, taken in conjunction with the accompanying drawings anddetailed description, wherein like reference numerals represent likeparts, in which:

FIG. 1 is a schematic drawing in elevation and section with portionsbroken away showing a rotary cone drill bit, incorporating features ofthe present invention disposed in a well bore;

FIG. 2 is a schematic drawing in section with portions broken awayshowing an exploded view of a bit body incorporating an embodiment ofthe present invention;

FIG. 3 is an enlarged schematic drawing showing an isometric view of adrill bit segment incorporating an embodiment of the present inventionduring an intermediate manufacturing step;

FIG. 4 is a schematic drawing in elevation showing a rotary cone drillbit fabricated from three drill bit segments incorporating an embodimentof the present invention during an intermediate manufacturing step;

FIG. 5 is a drawing in section taken along lines 5--5 of FIG. 4; and

FIG. 6 is a schematic drawing in elevation with portions broken awayshowing three drill bit segments incorporating teachings of the presentinvention with the drill bit segments aligned relative to each otherprior to welding.

DETAILED DESCRIPTION OF THE INVENTION

The preferred embodiments of the present invention and its advantagesare best understood by referring now in more detail to FIGS. 1-6 of thedrawings, in which like numerals refer to like parts.

The present invention may be embodied in a rotary cone drill bit 20 orany other type of drill bit formed from multiple segments and used indrilling a borehole in the earth. Rotary cone drill bit 20 may sometimesbe referred to as a "rotary drill bit" or "rock bit."Rotary cone drillbit 20 is shown in the drawings for purposes of illustration andpreferably includes threaded connection or pin 44 for attachment todrill string 22. Threaded connection 44 and a corresponding threadedconnection (not expressly shown) associated with drill string 22 aredesigned to allow rotation of drill bit 20 in response to rotation ofdrill string 22 at the well surface (not expressly shown).

As shown in FIG. 1, drill bit 20 may be attached to drill string 22 anddisposed in borehole 24. Annulus 26 is formed between the exterior ofdrill string 22 and interior wall 28 of borehole 24. In addition torotating drill bit 20, drill string 22 is often used to provide aconduit for communicating drilling fluids and other fluids from the wellsurface to drill bit 20 at the bottom of borehole 24. Such drillingfluids may be directed to flow from drill string 22 through enlarged,generally cylindrical cavity 30 (see FIG. 2) provided in drill bit 20 tovarious nozzles 60. Cuttings formed by drill bit 20 and any other debrisat the bottom of borehole 24 will mix with drilling fluids exiting fromnozzles 60 and return to the well surface via annulus 26. The debriscarrying fluid generally flows radially outward from beneath drill bit20 and then flows upward toward the well surface through annulus 26.

The present invention may be incorporated into the manufacture andassembly of a wide variety of rotary cone drill bits which arefabricated in part from drill bit segments. Drill bit 20, as shown inFIGS. 1 and 2, is preferably fabricated from three drill segments 40.Various welding techniques such as electron beam welding, laser weldingor any other suitable welding processes may be used to join drill bitsegments 40 with each other to form the associated drill bit 20.

For rotary cone drill bit 20, cutting action or drilling action occursas cutter cone assemblies 100, sometimes referred to as "rotary conecutters" or "roller cone cutters," are rolled around the bottom ofborehole 24 by rotation of drill string 22. Failure to maintain thedimensional relationship between cutter cone assemblies 100 withindesigned tolerances may substantially reduce the downhole performance ofthe associated rotary cone drill bit 20. Unequal loading of cutter coneassemblies 100 may result from inaccurate longitudinal or radialalignment of cutter cone assemblies 100 relative to each other duringfabrication of rotary cone drill bit 20. Such undesired variations inthe positioning of cutter cone assemblies 100 may result in poordownhole performance of the associated rotary cone drill bit 20.

Cutter cone assemblies 100 cooperate with each other to form interiorwall 28 or the inside diameter of borehole 24 in response to rotation ofdrill bit 20. The resulting inside diameter of borehole 24 defined bywall 28 corresponds approximately with the combined outside diameter orgauge diameter of cutter cone assemblies 100. Therefore, carefulpositioning of drill bit segments 40 and their associated cutter coneassemblies 100 relative to each is an important step to ensure that theresulting drill bit 20 will form borehole 24 with the required insidediameter. For some applications drilling fluid exiting from nozzles 60may apply hydraulic energy to the bottom borehole 24 to assist cuttercone assemblies 100 in forming borehole 24.

As shown in FIGS. 1-3, each cutter cone assembly 100 includes protrudinginserts 104 which scrape and gouge against the sides and bottom ofborehole 24 in response to the weight and rotation applied to drill bit20 from drill string 22. The position of inserts 104 for each cuttercone assembly 100 may be varied to provide the desired downhole cuttingaction. Cutter cone assembly 100 may be manufactured of any hardenablesteel or other high strength engineering alloy which has adequatestrength, toughness, and wear resistance to withstand the rigors ofdownhole drilling. Other types of cutter cone assemblies may besatisfactorily used with the present invention including, but notlimited to, cutter cone assemblies having milled teeth instead ofinserts 104. U.S. Pat. No. 5,579,856 entitled "Gage Surface and Methodfor Milled Tooth Cutting Structure" shows an example of a cutter coneassembly with milled teeth.

Three support arms 90 (FIG. 3) are shown attached to and extendinglongitudinally from bit body 42 opposite from threaded connection 44.Each support arm 90 preferably includes spindle 92 formed thereon andextending from second portion 80 of drill bit segment 40. One aspect ofthe present invention includes the ability to selectively position drillbit segments 40 relative to each other without substantially changingthe longitudinal position of cutter cone assemblies 100 relative to eachother. Longitudinal axis or centerline 32 extends through bit body 42and corresponds generally with the projected axis of rotation for drillbit 20.

Each cutter cone assembly 100 is preferably constructed and mounted toits associated spindle 92 in a substantially identical manner. Eachsupport arm 90 is preferably formed on second portion 80 of each drillbit segment 40 in substantially the same manner. Therefore, only onesupport arm 90 and cutter cone assembly 100 will be described in detailsince the same description applies generally to the other two supportarms 90 and their associated cutter cone assemblies 100.

Each drill bit segment 40 preferably includes first portion 50 which issized to be compatible with first portions 50 of other drill bitsegments 40 to form bit body 42. Each drill bit segment 40 also includessecond portion 80 which provides support arm 90 and respective spindleor journal 92. Support arm 90 which is formed on second portion 80 ofeach drill bit segment 40 extends longitudinally from bit body 42opposite from threaded connection 44.

Each cutter cone assembly 100 includes an internal cavity 102 shaped tobe rotatably mounted on the respective spindle or journal 92. For theembodiment shown in FIG. 2, thrust button 106 is disposed withininternal cavity 102 between the end of spindle 92 and the adjacent endof internal cavity 102. Journal bearing or bushing 108 is also disposedbetween the exterior of spindle 92 and the inside diameter of internalcavity 102. Elastomeric seal 110 is located at the opening or mouth ofinternal cavity 102 to provide a fluid seal between internal cavity 102and the adjacent portions of spindle 92. Seal gland 112 is also disposedoutwardly from elastomeric seal 110.

The present invention may be satisfactorily used with a wide variety ofbearing assemblies and sealing systems associated with mounting a cuttercone assembly on a respective spindle of a rotary cone drill bit. Thepresent invention is not limited to use with bearing assemblies andsealing systems such as shown in FIG. 2.

Cutter cone assembly 100 is retained on spindle 92 by a plurality ofballs or ball bearings 114 inserted through ball passage 116 formed inspindle 92. Lubricant cavity 118 is preferably formed within each drillbit segment 40. Lubricant reservoir 120 is preferably disposed withineach lubricant cavity 118. Lubricant passageway 122 and other suitableopenings and lubricant flow paths are preferably formed within secondportion 80 of each drill bit segment 40 to communicate lubricant betweeninternal cavity 102 and lubricant reservoir 120. Additional informationconcerning the lubricant system shown in FIG. 2 may be found in U.S.Pat. No. 5,513,715 entitled "Flat Seal for a Roller Cone Rock Bit."

The present invention may be satisfactorily used with rotary cone drillbits having a wide variety of lubricant systems and cutter cone assemblyretaining systems. The present invention is not limited to use withcutter cone assembly 100 or lubricant reservoir 120 as shown in FIG. 2.

One aspect of the present invention includes forming recess 70 having agenerally spherical configuration within each drill bit segment 40 at alocation selected in accordance with teachings of the present invention.When the respective drill bit segments 40 are joined with each other toform bit body 42, the respective spherical recesses 70 will cooperatewith each other to form a generally closed spherical cavity havingdimensions compatible with ball or ball bearing 72. The size ofspherical recess 70 and therefore, the size of ball bearing 72 will varyproportionally with the size of rotary cone drill bit 20.

Drill bit segment 40, incorporating one embodiment of the presentinvention, shown in FIG. 3 illustrates an intermediate manufacturingstep. Drill bit segment 40 is representative of only one type of drillbit segment which may be satisfactorily used to manufacture a rotarycone drill bit in accordance with teachings of the present invention.

As shown in FIGS. 2 and 3, each drill bit segment 40 has a generallyirregular, elongated configuration defined in part by first portion 50and second portion 80. Each drill bit segment 40 also includes anexterior surface and an interior surface extending from first end 46 tosecond end 48 of each drill bit segment 40. For purposes of explanationfirst portion 50 of drill bit segment 40 will be described as havinginterior surface 52 and exterior surface 54. In a similar manner, secondportion 80 of drill bit segment 40 will be described with respect tointerior surface 82 and exterior surface 84. However, as shown in FIGS.2 and 3, interior surfaces 52 and 82 cooperate with each other to definein part the interior surface of drill bit segment 40. In a similarmanner, exterior surfaces 54 and 84 cooperate with each other to definein part the exterior surface of drill bit segment 40.

Drill bit segment 40 may be formed from a suitable steel alloy such asAISI 8620 by forging or other suitable techniques. First portion 50 ofdrill bit segment 40 may sometimes be referred to as the "shank." Theportion of second end 48 where interior surface 82 joins exteriorsurface 84 may sometimes be referred to as the "shirttail."

As shown in FIGS. 1 and 3, an elongated channel 56 is preferably formedwithin interior surface 52 of first portion 50 of each drill bit segment40. Elongated channel 56 extend from first end 46 of each drill bitsegment 40 to a position adjacent to spherical recess 70. Elongatedchannels 56 cooperate with each other to allow forming enlarged,generally cylindrical cavity 30 within the resulting bit body 42 asshown in FIG. 4.

As shown in FIGS. 3 and 4, enlarged cavity 56 may be formed within firstportion 50 of drill bit segment 40. Fluids may be communicated betweenstring 22 and cavity 56. Cavity 56 preferably has a generally uniforminside diameter extending from first end 46 to a position intermediatefirst end 46 and second end 48 of drill bit segments 40. For someapplications, cavity 56 may be formed concentric with longitudinalcenterline 32 of drill bit segments 40.

As illustrated in FIG. 3, support arm 90 and journal or spindle 92 mayalso be machined from second portion 80 of each drill bit segment 40prior to forming bit body 42. Each spindle 92 includes longitudinal axis94 extending therethrough. The various bearing surfaces and sealingsurfaces associated with spindle 92 are preferably machined concentricwith longitudinal axis 94. Longitudinal axis 94 is typically used as areference point for establishing the various dimensions and tolerancesassociated with manufacturing drill bit segments 40 and fabricatingrotary cone drill bit 20. The dimensions of the associated interiorsurface 82 and exterior surface 84 may be selected depending upon thedesired dimensions for the resulting drill bit 20 and the respectivecutter cone assembly 100 which will be mounted on each respectivespindle 92.

A pair of mating surfaces 61 and 62, as shown in FIGS. 3 and 6, areformed on interior surface 52 of first portion 50 of each drill bitsegment 40. Elongated channel 56 is disposed between the respectivemating surfaces 61 and 62. For those applications in which three drillbit segments 40 are used to form bit body 42, mating surfaces 61 and 62are preferably formed at an angle of approximately one hundred andtwenty degrees (120°) relative to longitudinal centerline 32, as shownin FIG. 5. Longitudinal centerline 32 corresponds generally with theprojected axis of rotation of the resulting drill bit 20 when attachedto drill string 22. For those applications in which only two drill bitsegments are used to form the associated bit body, mating surfaces 61and 62 are preferably formed at an angle of approximately one hundredand eighty degrees (180°) relative to the longitudinal center line ofthe respective drill bit segments.

Various machining techniques may be used to insure that mating surfaces61 and 62 are compatible with corresponding mating surfaces 61 and 62 ofthe other drill bit segments 40 used to form bit body 42. For someapplications a V-shaped milling machine may be used to form matingsurfaces 61 and 62 on opposite sides of longitudinal centerline 32.

Mating surfaces 61 and 62 are formed generally parallel withlongitudinal centerline 32. Mating surfaces 61 and 62 are spaced fromeach other at first end 46 and intersect with each other at a locationintermediate first end 46 and second end 48 of each drill bit segment40. This intersection of mating surfaces 61 and 62 corresponds generallywith longitudinal centerline 32. As illustrated in FIGS. 2 and 3,generally spherical recess 70 is preferably formed on interior surface52 of each drill bit segment 40 at the intersection between first matingsurface 61 and second mating surface 62. Various milling techniques maybe used to form spherical recess 70.

Spherical recess 70 preferably has approximately the same radius in eachdrill bit segments 40 used to form bit body 42. Ball bearing 72 ispreferably selected to have a radius which is approximately equal to theradius associated with spherical recess 70. As a result, when drill bitsegments 40 are disposed adjacent to each other, such as shown in FIGS.4, 5 and 6, spherical recesses 70 cooperate with each other to form agenerally enclosed spherical cavity with ball 72 trapped therein.

After cutter cone assemblies 100 are mounted on their respectivespindles 92, mating surfaces 61 and 62 of drill bit segments 40 arepreferably positioned in a close abutting relationship with respect toeach other. FIG. 6 illustrates one such positioning of drill bitsegments 40 for a drill bit 20 having three drill bit segments 40. Awelding fixture (not expressly shown) may be used to clamp drill bitsegments 40 in their desired position prior to welding.

As shown in FIG. 3, notch 58 is preferably machined in first end 46 ofeach drill bit segment 40. Notch 58 and respective lugs (not expresslyshown) provided by an associated welding fixture (not expressly shown)may be used to initially position drill bit segments 40 relative to eachother within the welding fixture. A ring gauge (not expressly shown) maythen be positioned around cutter cone assemblies 100 and the exterior 84of second portion 80 of each drill bit segment 40 to establish thedesired composite outside diameter for rotary cone drill bit 20. Drillbit segments 40 may be moved or skewed relative to each other toestablish the desired gauge diameter. Such movement is particularlyrequired if the as-built dimensions for one or more drill bit segments40 varies from the designed dimensions.

Movement of drill bit segments 40 relative to each other may result in asliding or scissoring movement of mating surfaces 61 and 62 relative toeach other. For example, first end 46 may have irregularities such thatmovement of the associated drill bit segment 40 will result in asubstantial change in the longitudinal and radial positioning of theassociated cutter cone assembly 100. By placing ball bearing 72 withinspherical recesses 70, the position of drill bit segments 40 may beadjusted relative to each other to obtain the desired overall outsidediameter for drill bit 20 without substantially changing thelongitudinal position of cutter cone assemblies 100 relative to eachother. Without the use of recesses 70 and ball bearing 72, movement ofdrill bit segments 40 relative to each other results in a "scissoring"movement which may substantially alter the longitudinal position ofcutter cone assemblies 100 relative to each other. For someapplications, such movement of drill bit segments 40 relative to eachother may result in interference contact between respective cutter coneassemblies 100.

Placing ball bearing 72 within spherical recesses 70 also maintains thedesired general radial position of drill bit segments 40 relative toeach other. As best shown in FIG. 5, the position of each drill bitsegment 40 remains relatively concentric with respect to longitudinalcenterline 32. As a result, enlarged generally cylindrical cavity 30 maybe machined within of bit body 42 with a relatively uniform wallthickness. Without the use of spherical recesses 70 and ball bearing 72the scissoring movement associated with aligning drill bit segments 40relative to each other may result in a substantial offset of one or moreelongated channels 56 relative to longitudinal centerline 32. As aresult, when threaded connection 44 is machined on the exterior of bitbody 42, the wall thickness in the offset drill bit segment 40 may besubstantially reduced such that the associated drill bit 20 must bescrapped or reworked.

Interior surfaces 52 and 82 and exterior surfaces 54 and 84 may bemodified as desired for various downhole applications. The configurationof interior surfaces 52 and 82 and exterior surfaces 54 and 84 may bevaried substantially between first end 46 and second end 48 of drill bitsegment 40. Interior surface 82 and exterior surface 84 are contiguousat second end 48 of drill bit segment 40.

The size of drill bit 20 is determined by the maximum outside diameteror gauge diameter associated with the three cutter cone assemblies 100.The position of each cutter cone assembly 100 and their combined gaugediameter relative to the projected axis of rotation of drill bit 20 is afunction of the dimensions of drill bit segments 40, the associatedsupport arms 90 with cutter cone assemblies 100 mounted respectivelythereon, and the orientation of drill bit segments 40 relative to eachother.

Although the present invention has been described by severalembodiments, various changes and modifications may be suggested to oneskilled in the art. It is intended that the present inventionencompasses such changes and modifications as fall within the scope ofthe present appended claims.

What is claimed is:
 1. A rotary cone drill bit for forming a borehole,the drill bit comprising:a bit body formed from a number of drill bitsegments, each drill bit segment having a first portion and a secondportion; an interior surface formed on both the first portion and thesecond portion of each drill bit segment and an exterior surface formedon both the first portion and the second portion of each drill bitsegment; the first portion of each drill bit segment having two matingsurfaces formed on the interior surface thereof, the mating surfacessized to be compatible with respective mating surfaces of another drillbit segment disposed adjacent thereto; each drill bit segment having afirst end and a second end wherein the mating surfaces are spaced fromeach other at the first end and joined with each other intermediate thefirst end and the second end of the respective drill bit segment; agenerally spherical recess formed on the interior surface of each drillbit segment at the junction of the respective mating surfaces; asubstantially closed spherical cavity formed by the generally sphericalrecesses on the interior surfaces of each drill bit segment when themating surfaces of adjacent drill bit segments are joined together toform the bit body; and a ball disposed within the spherical cavitydefined by the spherical recesses.
 2. The drill bit of claim 1 furthercomprising a threaded connection formed on the bit body for attachingthe rotary cone drill bit to a drill string for rotation of the drillbit.
 3. The drill bit of claim 2 further comprising the threadedconnection formed on the exterior surface of the first portion of eachdrill bit segment after the drill bit segments have been welded to eachother to form the bit body.
 4. The drill bit of claim 2 furthercomprising an enlarged cavity formed within the first portion of thedrill bit segments for communicating fluids between the drill string andthe cavity.
 5. The drill bit of claim 2 wherein the second portion ofeach drill bit segment extends from the bit body opposite from thethreaded connection.
 6. The drill bit of claim 1 further comprising:aspindle attached to and projecting inwardly from the interior surface ofthe second portion of each drill bit segment; and a number of cuttercone assemblies with one cutter cone assembly being rotatably mounted oneach spindle.
 7. The drill bit of claim 1 wherein the mating surfaces ofeach drill bit segment are disposed at an angle of approximately onehundred and twenty degrees relative to a longitudinal centerline of therespective drill bit segment.
 8. The drill bit of claim 7 furthercomprising:the bit body having a longitudinal centerline correspondinggenerally with a projected axis of rotation of the drill bit; and thespherical cavity and the ball cooperate with each other to maintain anapproximately parallel alignment between the longitudinal centerline ofthe respective drill bit segment and the longitudinal centerline of thebit body.
 9. The drill bit of claim 1 further comprising:an elongatedchannel formed in the interior surface of the first portion of eachdrill bit segment; each elongated channel extending from the respectivefirst end to a position adjacent to the generally spherical recess; andthe elongated channels cooperating with each other to define a generallycylindrical cavity in the bit body for receiving fluids from a drillstring attached to the drill bit.
 10. The drill bit of claim 1 furthercomprising:a first radius associated with each generally sphericalrecess formed on the interior surface of each drill bit segment; and asecond radius associated with the ball disposed within the sphericalcavity, the second radius of the ball being approximately equal to thefirst radius of each spherical recess.
 11. A drill bit segment for usein forming a rotary cone drill bit, the drill bit segment comprising:afirst end and a second end with a first portion and a second portiondisposed therebetween; an exterior surface formed on the first portionand the second portion extending from the first end to the second end;an interior surface formed on the first portion and the second portionextending from the first end to the second end; two mating surfacesformed on the interior surface of the first portion and sized to becompatible with corresponding mating surfaces of a drill bit segmentdisposed adjacent thereto; the mating surfaces spaced from each other atthe first end and joined with each other intermediate the first end andthe second end of the drill bit segment; and a generally sphericalrecess formed on the interior surface of the drill bit segment at thejunction of the respective mating surfaces and sized to receiveapproximately one-third of a ball disposed therein during assembly ofthe drill bit segment with two other corresponding drill bit segments.12. The drill bit segment of claim 11 further comprising:an elongatedchannel formed in the interior surface of the first portion disposedbetween the mating surfaces; and the elongated channel extending fromthe first end to a position adjacent to the generally spherical recess.13. The drill bit segment of claim 11 further comprising:a spindleattached to and projecting inwardly from the interior surface of thesecond portion; and a cutter cone assembly rotatably mounted on thespindle.
 14. The drill bit segment of claim 11 further comprising anotch formed in the first end.
 15. A method of fabricating a rotary conedrill bit from multiple drill bit segments wherein each drill bitsegment has a first end and a second end and two mating surfaces formedon an interior surface of the respective drill bit segment, the methodcomprising:forming a spherical recess in each drill bit segment at anintersection of the respective mating surfaces intermediate the firstend and the second end; placing a ball in one of the spherical recesses;and positioning the drill bit segments adjacent to each other such thata portion of the ball is disposed in each of the respective sphericalrecesses and the mating surfaces of adjacent drill bit segments are inclose proximity to each other to accommodate welding the drill bitsegments together to form a bit body for the rotary cone drill bit. 16.The method of claim 15 further comprising the step of forming the bitbody from three drill bit segments.
 17. The method of claim 15 furthercomprising the steps of:forming each drill bit segment with alongitudinal center line extending therethrough; and forming the matingsurfaces at an angle of approximately one hundred and twenty degreesrelative to the longitudinal center line.
 18. The method of claim 15further comprising the steps of forming each spherical recess and theball with approximately the same radius.
 19. The method of claim 15further comprising the step of adjusting the position of the drill bitsegments relative to each other to establish a desired outside diameterfor the rotary cone drill bit prior to welding the drill bit segmentswith each other.
 20. The method of claim 15 further comprising the stepof forming a notch in the first end of each drill bit segment.